1. Field of the Invention
The invention relates to an image forming apparatus such as a copying machine, a printer or a facsimile apparatus, and particularly to an electrophotographic image forming apparatus which can reverse the front side and the back side of copy paper on which an image has been fixed by heat and re-feed the copy paper to an image forming portion.
2. Description of Related Art
FIG. 7 of the accompanying drawings is a cross-sectional view of a digital copying machine as a conventional image forming apparatus.
A digital copying machine main body 1 is comprised of a reader 2 for reading the image of a document, and a printer 3 for forming an image on copy paper, and an auto document feeder 4 for successively feeding documents stacked thereon to a predetermined position on the reader 2 is connected to the reader 2.
A bundle of documents are stacked on the document stacker 401 of the auto document feeder 4 with the image surface of the head page facing upward, and are fed in succession from the uppermost document by the rotative driving of a document feed roller 402.
The thus fed document is placed on a document glass plate 201 with its image surface facing downwardly, and image reading by the reader 2 is effected. The image reading by the reader 2 is effected by a well-known technique of irradiating the document by an illuminating lamp 202, and imaging reflected light from the document on a CCD sensor in an image sensor 207 through the intermediary of reflecting mirrors 203, 204, 205 and a lens 206. As the reading operation at this time, there are two ways, i.e., the operation of reading with a scanner unit 208 comprising the illuminating lamp 202, the reflecting mirror 203, etc. moved relative to the documents stationarily placed on the document glass plate 201 (stationary document reading mode), and the operation of reading by the scanner unit 208 stationary relative to the document moving on the document glass plate 201 (flowing document reading mode), and the reading operation is selectively changed over in conformity with the mode, whereby the document reading time is shortened to thereby achieve an improvement in productivity. The documents of which the image reading by the reader 2 has been finished are successively delivered onto a document delivery tray 403 with their image surfaces facing downwardly.
A plurality of image data read by the above-described operation are all stored in a large-capacity memory (hard disc), not shown, and the image data stored in the memory are outputted to the printer 3 in the order conforming to an editing mode designated by the operating portion (not shown) of the digital copying machine 1.
Copy sheets which are recording mediums for the read images are contained in a right deck 301, a left deck 302, an upper cassette 303, a lower cassette 304 an a manual feed tray 305. The copy sheets successively fed one by one of feed rollers 306-310 being selectively rotatively driven are supplied to an image forming portion while being timed by registration rollers 311. In the image forming portion, a photosensitive drum 312 is rotated in the direction indicated by the arrow in FIG. 7 by a motor (not shown) and is charged to desired potential by a primary charger 313, and thereafter is subjected to the application of a predetermined laser beam based on image data, whereby an electrostatic latent image is formed on the photosensitive drum 312, and the electrostatic latent image is developed as a toner image by a developing device 315. As a developing process at this time, there is well known a triboelectrification process comprising agitating and conveying a magnetic toner stored in a developing device 315, attracting it to a rotary developing sleeve 317 on which a magnetic pole pattern (strength and weakness of a magnetic force) has been formed in the circumferential direction, thinly and uniformly regulating an amount of coat by a developing blade 318 of a magnetic material disposed with a uniform minute gap in the lengthwise direction of the developing sleeve and also, causing the toner to rub in an agitating portion and a minute gap portion to thereby impart predetermined charges thereto. The developed toner image is transferred to the supplied copy paper by a transfer charger 319, and the photosensitive drum 312 after the termination of the transfer has any residual toner thereon removed by a cleaner 320, and has any residual charges thereon eliminated by a pre-exposure lamp 321. The toner collected by the cleaner 320 is conveyed to a waste toner bottle (not shown) by a conveying portion such as a screw 322. The copy paper after the termination of the transfer is stripped from the photosensitive drum 312 by a stripping charger 323, is transported to a fixing roller 325 by a transport belt 324, and is subjected to pressure and heating by the fixing roller 325, whereby the toner image on the copy paper is fixed as a permanent image.
When a single-sided copy mode is selected by an operating portion (not shown), the copy paper on which the toner image has been fixed is delivered onto a delivery tray 331 by delivery rollers 330 via a straight delivery path 333.
On the other hand, when a two-sided copy mode is selected by the operating portion (not shown), the copy paper of which the toner image on the first side has been fixed is once drawn into a surface reverse portion 327 via a surface reverse transport path 326, and thereafter goes via a duplex transport path 332 by the reverse rotation of surface reverse rollers 328, whereby it is again supplied to the image forming portion with the upper side and the lower side of the copy paper reversed, and an image on the second side is formed. The copy paper of which the toner images on the two sides have been fixed goes via the straight delivery path 333 and is delivered onto the delivery tray 331 by the delivery rollers 330.
In the above-described image forming apparatus, however, when in the two-sided copy mode, there is a case where copy paper heated by the fixing roller is again supplied to the image forming portion in a state in which it is not sufficiently cooled, there has been the undesirable possibility that the toner in the developing device rises in temperature due to the heat radiation from the copy paper and the chargeability thereof is deteriorated and such abnormal image as thin image density occurs.
Also, in cases where, due to heat radiation from copy paper during two-sided copying, the toner in the developing device rises in temperature beyond a fusing point, there is the undesirable possibility that the fused toner is fused to the developing sleeve or the developing blade and the amount of toner coat on the developing sleeve becomes non-uniform and an abnormal image such as uneven image density or a streaked image occurs.
Further, in cases where the fuse toner is fused and bonds to a toner conveying member such as the agitator of the developer or the screw of the cleaner, there is also the undesirable possibility that the conveyance of the toner is hindered or faulty operation due to the rise of a driving load is caused.
Particularly, with the recent tendency toward higher speed image forming apparatus, the time from when copy paper has passed the fixing roller until it again arrives at the image forming portion becomes shorter, and the time for which the heat of duplex copy paper is diffused in a machine and cooled is decreased, and the quantity of heat imparted to the toner in the developing device and the cleaner per unit time tends to increase more and more.
In order to solve the problem of the temperature rise of the toner in the developing device and the cleaner attributable to the heat of the duplex copy paper, there have heretofore been proposed various techniques of disposing a copy paper cooling portion in a transport route downstream of a fixing roller.
As an example of them, as disclosed in Japanese Patent Application Laid-Open No. 7-242370, there is a technique of disposing a blower portion such as a fan downstream of a fixing roller, and directly blowing a cooling wind against duplex copy paper, but if the air flow rate of the fan is too strong, there may occur bad conveyance such as paper breakage, paper wrinkling or jam due to the fluttering of the copy paper, and the air flow rate of the fan is limited to such a level that the above-noted problems do not arise and therefore, the cooling capability thereof has been limited.
Also, as disclosed in Japanese Patent Application Laid-Open No. 4-46451, there is a technique of disposing a heat absorbing portion such as a heat pipe downstream of a fixing roller, contacting with duplex copy paper directly or through a conveying belt or a conveying guide to thereby effect heat absorption, and cooling a radiating portion disposed in a space independent of a paper transport area by a blower portion such as a fan, but the contact area of a heat transmitting portion is limited by the diameter of the heat pipe and therefore, the cooling capability thereof has been limited or the bulkiness of the apparatus has resulted.
An embodiment of the present invention has been made in view of the above-noted problem, and an object thereof is to provide an image forming apparatus which does not result in faulty transport or the bulkiness of the apparatus due to the fluttering of copy paper and which can sufficiently cool the heat of duplex copy paper without limiting the cooling capability of even an image forming apparatus in which higher speed requiring higher cooling capability has been realized or the fixing temperature has become high, and which can prevent a faulty image and a faulty operation due to the temperature rise of a toner in a developing device and a cleaner in a two-sided copy mode.
In order to achieve the above object, the image forming apparatus according to the present invention is an image forming apparatus having an image forming portion for forming an image on copy paper fed thereto, a fixing portion for heating and fixing the image formed on the copy paper by the image forming portion, and a transporting portion for transporting the copy paper on which the image has been fixed by the fixing portion, and is characterized in that in the transporting portion, there are disposed at least one heat absorbing portion for contacting with the copy paper and absorbing the heat of the copy paper, and at least one cooling portion for cooling the heat absorbing portion.
Other objects and features of the present invention will become apparent from the following description and the accompanying drawings.